This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-269251, filed on Sep. 5, 2000; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for preparing an oxide superconductor, a raw material for an oxide superconductor, and a method for preparing a raw material for an oxide superconductor. The present invention relates in particular to a method for preparing an oxide superconductor, a raw material for an oxide superconductor, and a method for preparing a raw material for an oxide superconductor, all employing a metal trifluoroacetate.
2. Description of the Related Art
Oxide superconductors are expected to use in a variety of applications such as superconducting coils, superconducting magnets, nuclear fusion reactors, magnetic levitation trains, accelerators, magnetic imaging systems (Magnetic Resonance Imaging systems or the like), superconducting magnetic energy storage or the like, some of these being put into practical use.
There are bismuth-based and yttrium-based superconductors in the oxide superconductors, due to few deterioration such as critical current density or the like even under a magnetic field, the yttrium-based superconductors drawing attention.
As the methods for preparing the yttrium-based superconductors, there are a variety of methods such as pulsed laser deposition, liquid phase epitaxy method and electron beam evaporation. Among these, metal organic deposition is attracting attention because it can disuse a vacuum and facilitates to prepare the oxide superconductors at low costs. Of the metal organic deposition, metal-organic deposition method using trifluoroacetates (hereafter refers to as xe2x80x9cTFA-MOD methodxe2x80x9d), due to its simplicity, is drawing attention of its future.
As the TFA-MOD method, a method where metal acetate and water are starting materials has been tried by Gupta (cf. A. Gupta, et al, Appl. Phys. Lett. vol. 52 (No.24), page 2077 (1988)) or by McIntyre and Cirma (cf. P. C. McIntyre, et al, Appl. Phys. vol. 68 (No.8), page 4183 (1990)).
The oxide superconductors are preferable to be high in performance (for instance, to be high in the critical current density while having a certain thickness). However, it is difficult to prepare, from starting materials of metal acetate and water, an oxide superconductor which has for instance a thickness of 0.1 xcexcm or more and exceeds 1 MA/cm2 in the critical current density.
An object of the present invention is to provide a method for preparing an oxide superconductor that can make use of metal acetates as the starting material and exhibits high performance.
(1) A method for preparing an oxide superconductor involving one embodiment of the present invention includes:
mixing an aqueous solution of mixed metal acetate containing one kind or more metal element selected from lanthanide series and yttrium, barium and copper and trifluoroacetic acid to prepare an aqueous solution of mixed metal trifluoroacetate;
purifying the aqueous solution of mixed metal trifluoroacetate prepared according to the mixing to prepare purified mixed metal trifluoroacetate in which a total content of water and acetic acid is two % by weight or less;
dissolving the mixed metal trifluoroacetate prepared according to the purifying in a solvent to prepare a coating solution;
coating the coating solution prepared according to the dissolving on a base material to prepare a film of the mixed metal trifluoroacetate; and
heating the base material thereon the film of the mixed metal trifluoroacetate is formed according to the coating to prepare a superconductor.
The total content of water and acetic acid of 2% by weight or less in the purified mixed metal trifluoroacetate enables to prepare the oxide superconductors of excellent performance.
The purifying may includes:
a first refining process in which the solution of mixed metal trifluoroacetate prepared according to the mixing is refined under a reduced pressure to prepare a first purified mixed metal trifluoroacetate in which water and acetic acid are reduced;
addition of a substance capable of replacing water and acetic acid in the first purified mixed metal trifluoroacetate to the first purified mixed metal trifluoroacetate prepared according to the first refining process; and
a second refining process in which the first purified mixed metal trifluoroacetate thereto the replaceable substance is added according to the addition is refined under a reduced pressure to prepare the second purified mixed metal trifluoroacetate in which water and acetic acid are reduced.
In the second purified mixed metal trifluoroacetate prepared by adding the replaceable substance to the first purified mixed metal trifluoroacetate and by refining under a reduced pressure, larger part of the water and acetic acid in the first purified mixed metal trifluoroacetate is replaced by the replaceable substance. As a result, the total content of the water and acetic acid in the second purified mixed metal trifluoroacetate is reduced in comparison with that of the water and acetic acid in the first purified mixed metal trifluoroacetate. By the use of the second purified mixed metal trifluoroacetate, the superconductors of excellent performance may be formed.
(2) Raw material for an oxide superconductor involving one embodiment of the present invention includes:
mixed metal trifluoroacetate containing one kind or more metal selected from the lanthanide series and yttrium, barium and copper;
wherein the total content of water and acetic acid is 0.5% by weight or less with respect to the mixed metal trifluoroacetate.
In the raw material for oxide superconductor, metal acetates each may be mixed with an appropriate mixing ratio as demands arise. Thereby, the raw material for oxide superconductor may be used for preparing the oxide superconductor of Y123 system. The total content of the water and acetic acid of 0.5% by weight or less in the raw material enables to prepare the oxide superconductor of excellent performance.
(3) A method for preparing raw material for oxide superconductors involving one embodiment of the present invention includes:
mixing an aqueous solution of metal acetate containing one kind or more metal element selected from lanthanide series and yttrium, barium and copper with trifluoroacetic acid to prepare a solution of metal trifluoroacetate;
a first refining process of the metal trifluoroacetate solution prepared according to the mixing under a reduced pressure to prepare a first purified metal trifluoroacetate in which water and acetic acid are reduced;
adding a substance capable of replacing water and acetic acid in the first purified metal trifluoroacetate to the first purified metal trifluoroacetate prepared according to the first refining process; and
a second refining process of the first purified metal trifluoroacetate thereto the replaceable substance is added according to the addition under a reduced pressure to prepare a second purified metal trifluoroacetate in which the total content of water and acetic acid is 2% by weight or less.
By means of the first refining process, the addition, and the second refining process, the second purified metal trifluoroacetate is prepared to be 2% by weight or less in the total content of water and acetic acid, being used as mixed raw material for preparing a superconductor of excellent performance.